The aim of this application is the elucidation of the functional role of four novel binding proteins for a presynaptic-acting snake venom toxin, taipoxin, that blocks synaptic vesicle recycling. Three of these proteins (neuronal pentraxin 1, NP1; neuronal pentraxin 2, NP2; and neuronal pentraxin receptor, NPR) have homology to acute phase proteins, C-reactive protein and serum amyloid P protein that recognize bacteria and cell debris. We propose that these neuronal pentraxins represent a novel neuronal uptake pathway that may be associated with synaptic formation and remodeling and potentially AMPA receptor clustering. The fourth protein is a novel reticular calcium- binding protein, taipoxin-associated calcium binding protein 49 (TCBP49). To test the function of these proteins and to test our hypothesis that these proteins form a pathway for synaptic uptake, we will undertake the following experiments. First, we will test if all neuronal pentraxins are localized to synapses and whether their message expression follows synaptogenesis. Second, we will test for alterations of synapses, synaptic physiology and taipoxin action in mice that lack neuronal pentraxins. Third, we will test the role of TCBP49, NP1, NP2 and NPR in taipoxin blockade of endocytosis in CHO and PC12 cells transfected to express these proteins or express antisense RNA. Fourth, we will expand our chromatographies to investigate proteins that interact with glycosylated, homo- and heteropentameric NP1, NP2 and NPR to test the connection of these proteins to the endocytic AP-2 clathrin adaptor complex and to AMPA receptors.